Field of the Invention
This invention relates to optically active alcohols and their derivatives having two asymmetric centers, liquid crystal compositions containing said optically active compounds and liquid crystal devices thereof.
The technology of liquid crystal displays has been developed rapidly in the last two decades due to the invention of novel nematic liquid crystals, the discovery of their electro-optic effects and extensive development in electronic industries. The application of liquid crystal displays has been extended from the simple display in electronic watches to the display of personal computers and even has a great potential in the development of the display of high definition television. Although liquid crystals are of wide application, further improvements are desired so as to improve their contrast, view angle and their switching speed.
In 1975 Meyer et. al. found that chiral smecticC phase is ferroelectric after a series of experiments conducted on p-(decyloxy) benzylidene-amino-2-methylbutyl-cinnamate (R. B. Meyer, L. Liebert, L. Strzeleckl and P. Keller, "Ferroelectric Liquid Crystals" J. Physique Lett., 1975, 36, L69). Since then, the development and the application of such smectic phase liquid crystals have become a challenging research field. In 1980 Clark and Lagerwall invented a device employing such liquid crystals, i.e., an SSFLC (surface-stabilized ferroelectric liquid crystal) light valve which is a basic device for new electro-optic technology (N. A. Clark, S. T. Lagerwall, Appl. Phys. Lett., 1980, 36, 899). Since the ferroelectric liquid crystals exhibits unique switching speed and memorizable characteristics, they are in great demand for application in optical-switches, optical-calculators, flat displays, etc.
The ferroelectricity of ferroelectric liquid crystals are mainly contributed by the optically active molecular part of the liquid crystals formed by asymmetric synthesis. Ferroelectric liquid crystal displays generally employ a mixture of liquid crystals in which chiral compounds are used as chiral dopant. The chiral dopant may or may not have chiral smectic C phase (W. Kuczynski, H. Stegemeyer, Chem. Phys. Lett., 1980, 70, 123; F. Leenhouts, S. M. Kelly, A. villiger, Displays, 1990, 41). Intrinsically ferroelectric liquid crystal is also one of nonlinear optical which are now under intensive study worldwide.
Lactic acid is a commercially available optically active material which consists of easily convertible functional groups, i.e., hydroxy and carboxy groups, which can be easily converted into other molecular structures. U.S. Pat. Nos. 4,556,727, 4,812,259, 4,880,560, 4,961,875, and 4,985,172 disclose optically active lactic derivatives and their application in liquid crystal compositions and liquid crystal devices. These patents also disclose that liquid crystal materials containing two asymmetric centers have better physical properties than those containing only one asymmetric center.